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This week I’m talking about the plea of insanity – hopefully not for future reference. For legal purposes, insanity means either that a person was labouring under natural imbecility or disease of the mind at the time of the offence, or that they are unfit to stand trial. The defence is not limited to homicide, but it is primarily used in such instances because a successful plea often results in involuntary incarceration, and this can be more oppressive than a conviction.

The law has long recognised insanity as a defence. In 1798, a Mr. Hadfield attempted to assassinate King George III. Already suffering from delusions after sustaining multiple head injuries at war, Hadfield joined a religious cult. Needless to say, this only served to exacerbate his delusions. Hadfield thought that killing the King would bring about religious revolution, and attempted to shoot him. The judge was of the view that Hadfield acted with a degree of premeditation in reliance on his delusions, and he was acquitted on that basis. The M’Naghten Rules arose from similar circumstances in 1843, and a revised version of those rules has been incorporated into our Crimes Act.

In New Zealand, the defence is available where a person laboured under natural imbecility or disease of the mind at the time the offence was committed. Adams on Criminal Law provides that “a finding of not guilty on the ground of insanity will ensure that someone who has no criminal intent or capacity to form a criminal intent due to mental illness, is not regarded or treated as criminal.” The plea was successful for one man who shot a police officer in “self defence”, believing him to be a KGB infiltrator. Although a mistaken and delusional belief, it was rationally held by him.

After a successful plea, one may be incarcerated on the grounds of mental illness, contrary to what is sometimes depicted on below-par crime shows where the defendant walks free after being found not guilty by way of insanity. Through the relevant mechanisms, the person is monitored and treated until such supervision is no longer required. Detention as a “special patient” may be made under the corresponding legislation. Alternatively, detention in hospital may be ordered under compulsory community psychiatric care on either an inpatient or outpatient basis. Immediate release is less common and only ordered where special circumstances arise. This happened in 1998, when release was in the best interests of the public as the peculiar circumstances (including a mix-up with medication) were unlikely to repeat themselves.

– Alice O’Connell